Other posts will be allowed to reopen as normal on Monday, including ones in Dhaka, Algiers, Nouakchott, Kabul, Herat, Mazar el Sharif, Baghdad, Basrah, and Erbil.

Police presence around the U.S. Embassy in Cairo remained high Sunday as more than 20 U.S. embassies and consulates across the region closed and a worldwide travel alert remained in effect because of a terrorist threat.

The travel alert, effective until the end of the month, warned U.S. citizens that al-Qaeda and affiliated groups continue to plan terrorist attacks particularly in the Middle East and North Africa. Meanwhile, international police agency Interpol issued a global security alert on Saturday advising increased vigilance after a series of prison breaks with suspected al-Qaeda involvement in countries including Iraq, Pakistan and Libya.

"We may be seeing an effort, a trend, of al-Qaeda trying to announce its relevance, trying to show the world it's still in the game," said Frederic Wehrey, a senior associate in the Middle East Program at the Carnegie Endowment for International Peace. "And some sort of spectacular attack on a U.S. facility would certainly do that."

Sen. Saxby Chambliss, R-Ga., said Sunday the weekend closures were the result of the "most serious threat" he'd seen in recent years. Chambliss told NBC's Meet the Press that the intelligence was "very reminiscent of what we saw pre-9/11."

Rep. C.A. Dutch Ruppersberger, D-Md., told ABC's This Week that the threat intercepted from "high-level people in al-Qaeda in the Arabian Peninsula" was about a "major attack."

"The threat was specific as to how enormous it was going to be and also that certain dates were given," Rep. Pete King, R-N.Y., who chairs a House panel on counterterrorism and intelligence, told ABC.

Meanwhile, extra security was noted as several U.S. embassies, including those in Yemen, Jordan, Bahrain and Iraq.

In the Jordanian capital of Amman, a Jordanian security officer told The Associated Press that bomb squads searched the perimeter of the U.S. Embassy while additional security vehicles were deployed in the area, including troop carriers with special forces trained in counterterrorism. Security also was tightened around the homes of U.S. diplomats in Amman, said the officer, who spoke on condition of anonymity in line with regulations.

This week marks the 15th anniversary of terrorist attacks on U.S embassies in Nairobi, Kenya and Tanzania that killed hundreds of people.

On Saturday, top U.S. security advisers including FBI, CIA and National Security Agency directors, Secretary of State John Kerry, Secretary of Defense Chuck Hagel and Gen. Martin Dempsey - the chairman of the Joint Chiefs of Staff - met to review the threat.

"Early this week, the president instructed his national security team to take all appropriate steps to protect the American people in light of a potential threat occurring in or emanating from the Arabian Peninsula," the White House said in a statement.

National Security adviser Susan Rice chaired the team's meeting Saturday afternoon to further review the situation and discuss follow-up actions, the statement said.

Dempsey, in a Friday interview with ABC News, said officials determined "a significant threat stream" and found the "intent is to attack Western, not just U.S. interests."

France, Germany and the United Kingdom also closed their embassies in Yemen on Sunday, the start of the work week in the region.

Seth Jones, associate director of the International Security and Defense Policy Center at the RAND Corp., said he suspects the U.S. embassy closings are tied to active plotting against multiple locations and concern over a high threat level based on credible intelligence.

"It's easier (for al-Qaeda) to target a U.S. embassy in the region where it has now, in several areas, a growing presence, or allies and affiliates that have a growing presence, than it is to try to get operatives to go to the U.S. homeland to conduct attacks," Jones said.

The wide-scale embassy closings may also reflect that the U.S. diplomatic corps and State Department have less tolerance for uncertainty, analysts said. U.S. Ambassador to Libya Chris Stevens and three other Americans died in an attack on the U.S. consulate in Benghazi, Libya, on Sept. 11.

"In the wake of the Benghazi attack they're just not going to take any chances," said Wehrey, an expert on security in the region.

Last year's violence in Libya occurred alongside an attack on Cairo's U.S. Embassy as protesters scaled the compound's walls and took down the American flag.

Egyptian security forces at the time did little, if anything, to halt the attack. But soon after the violence, authorities built massive, concrete-block walls to secure roads leading to the compound and boosted other security measures.

On Sunday, those blocks remained in place and many police were standing by, although shop owners in the embassy area said there were no visible signs of an increased security presence.

"It's exactly like it is every day," said Ahmed Fathy, who owns a pharmacy across the street from the embassy.